Flexible stent and method of manufacture

ABSTRACT

A preferred embodiment of a stent provides a folded strut section that provides both structural rigidity and reduction in foreshortening of the stent mechanism. A flexible section provides flexibility for delivery of the stent mechanism. In a second embodiment, flexible section columns are angled with respect to each other, and to the longitudinal axis of the stent. These relatively flexible sections are oppositely phased in order to negate any torsion along their length. In yet another embodiment, the flexible connector can take on an undulating shape (like an “N”), but such that the longitudinal axis of the connector is not parallel with the longitudinal axis of the stent. Finally, a new method is disclosed for making stents. The method consists of performing a standard photochemical machining process of cutting, cleaning and coating the tube with a photoresist. However, unlike former methods, the photoresist image is developed on the surface of the cylindrical metallic tube, which results in a controlled variable etching rate at selected sites on the cylindrical metallic tube during the etching process. Further embodiments provide living hinge connectors and connections along the length of the radial strut member.

PRIORITY

This application claims priority from Ser. No. 60/272,696, entitled“Flexible Stent and Method of Manufacture”, filed Mar. 1, 2001.

BACKGROUND ART

A stent is commonly used as a tubular structure left inside the lumen ofa duct to relieve an obstruction. Commonly, stents are inserted into thelumen in a non-expanded form and are then expanded autonomously (or withthe aid of a second device) in situ. A typical method of expansionoccurs through the use of a catheter mounted angioplasty balloon, whichis inflated within the stenosed vessel or body passageway, in order toshear and disrupt the obstructions associated with the wall componentsof the vessel and to obtain an enlarged lumen.

In the absence of a stent, restenosis may occur as a result of elasticrecoil of the stenotic lesion. Although a number of stent designs havebeen reported, these designs have suffered from a number of limitations.These include restrictions on the dimension of the stent.

Other stents are described as longitudinally flexible but consist of aplurality of cylindrical elements connected together. This design has atleast one important disadvantage, for example, according to this design,protruding edges occur when the stent is flexed around a curve raisingthe possibility of inadvertent retention of the stent on plaquedeposited on arterial walls. This may cause the stent to form emboli ormove out of position and further cause damage to the interior lining ofhealthy vessels.

Thus, stents are known in the art. Such stents may be expanded during orjust after balloon angioplasty. As a general rule, the manufacture of astent will need to compromise axial flexibility in order to permitexpansion and provide overall structural integrity.

Prior stents have had a first end and a second end with an intermediatesection between the two ends. The stent further has a longitudinal axisand comprises a plurality of longitudinally disposed bands, wherein eachband defines a generally continuous wave along a line segment parallelto the longitudinal axis. A plurality of links maintains the bands in atubular structure. In a further embodiment of the invention, eachlongitudinally disposed band of the stent is connected, at a pluralityof periodic locations, by a short circumferential link to an adjacentband. The wave associated with each of the bands has approximately thesame fundamental spatial frequency in the intermediate section, and thebands are so disposed that the waves associated with them are spatiallyaligned so as to be generally in phase with one another. The spatialaligned bands are connected, at a plurality of periodic locations, by ashort circumferential link to an adjacent band.

In particular, at each one of a first group of common axial positions,there is a circumferential link between each of a first set of adjacentpairs of bands.

At each one of a second group of common axial positions, there is acircumferential link between each of a second set of adjacent rows ofbands, wherein, along the longitudinal axis, a common axial positionoccurs alternately in the first group and in the second group, and thefirst and second sets are selected so that a given band is linked to aneighboring band at only one of the first and second groups of commonaxial positions.

Furthermore, this stent can be modified to provide for bifurcatedaccess, whereas the stent itself is uniform throughout. If themanufacturer designs such a stent to have an large enough opening, thenit is possible to place the stent such that a pair of stents can beplaced one through the other. In this fashion, the stents are capable ofbeing placed at a bifurcation, without any welding or any specialattachments. An interlocking mechanism can be incorporated into thestent design to cause the stent to interlock at the desired positionduring assembly of the device.

Further, a metallic stent has been designed which contains a repeatingclosed loop feature. The stent is designed such that the closed loopdoes not change dimensions during expansion. The composite stent iscreated by filling the area enclosed by the loops with a material thatenhances clinical performance of the stent. The material may be aceramic or a polymer, and may be permanent or absorbable, porous ornonporous and may contain one or more of the following: a therapeuticagent, a radio-opaque dye, a radioactive material, or a material capableof releasing a therapeutic agent, such as rapamycin, cladribine,heparin, nitrous oxide or any other know drugs, either alone or incombination.

It has been seen, however, that it may be desirable to provide forstents that have both flexibility to navigate a tortuous lesion as wellas increased column strength to maintain the rigidity necessary afteremplacement into the lumen of the body. The preferred designs tend toprovide the flexibility via undulating longitudinal connectors. Therigidity is generally provided via the mechanism of slotted tubularstents. It is perceived that there may be mechanisms capable ofenhancing the characteristics of these types of stents. Such a stentwould be both flexible in delivery and rigid upon emplacement.

Furthermore, it is desirable to be able to produce stents in which thecross-sectional profile of either the struts or the connecting membersis tapered (or variable) in size. In addition, it may be desirable tomodify stents to have non-rectangular cross-sections. In both thesecases, different manufacturing methods may aid in the creation of suchstents.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a stent having hasrelatively little foreshortening.

It is an object of the invention to provide a stent having an enhanceddegree of flexibility.

It is an object of the invention to provide such a stent whilediminishing any compromise in the stent's structural rigidity uponexpansion.

It is a further object of the invention to provide a novel method formanufacturing stents.

These and other objects of the invention are described in the followingspecification. As described herein, a preferred embodiment of a stentprovides for a device that contains a flexible section and a foldedstrut section. The folded strut section opens (like a flower) uponexpansion. This folded strut section provides both structural rigidityand reduction in foreshortening of the stent mechanism. The flexiblesection provides flexibility for delivery of the stent mechanism.

In a second embodiment of the device, there is a columnar section and aflexible section. The columnar section provides for a device thatlengthens in the longitudinal direction upon expansion. The flexiblesection provides for a section that shortens somewhat in thelongitudinal direction upon expansion. As a result, there is noshortening or lengthening of the stent during expansion. The flexiblesection columns are angled, one with respect to the other, and also withrespect to the longitudinal axis of the stent, in order to provideflexibility during delivery. This arrangement also to also provideadditional resistance to the balloon to prevent “dogboning” of the stenton the balloon during delivery and slippage of the balloon along thestent. These relatively flexible sections are oppositely phased withrespect to one another in order to negate any torsion along theirlength. These flexible sections can further be crimped onto the ballooncatheter with a generally smaller profile than prior stent, so that theretention of the stent on the balloon is increased.

In yet another embodiment of the stent of the present invention, theflexible connector can take on an undulating shape (like an “N”), butsuch that the longitudinal axis of the connector is not parallel withthe longitudinal axis of the stent. In this fashion, the flexibility iscontrolled in a pre-selected axis, which is not the longitudinal axis ofthe stent. Such an arrangement may be desired, for instance, when onechooses to place a stent in a particularly configured vasculature thathas been predetermined by known means, such as intravascular ultrasound(“IVUS.”)

In still a further embodiment of the present invention, there areprovided “living hinge” connectors, which connect the generally flexibleconnectors to the stronger radial strut members. These living hingesaccomplish a number of the same characteristics found in the priorembodiments disclosed herein. First, because the living hinges tend toexpand upon inflation, foreshortening of the length of the stent isfurther reduced. Second, there is a combined radial strength provided atthe intersection between the living hinges and the radial strut members.This creates a small “hoop,” which is further resistant to kinking orcollapse in situ. Third, as a corollary to the second attributedescribed above, the living hinge connectors provide for reduced strainalong an equivalent length of stent.

In yet another preferred embodiment of the stent of the presentinvention, the connection point between the radial members and theconnector members is moved to a position along the length of a radialstrut. Typically, the connection may be placed at a position somewheremidway along the length of the strut. By moving the connection point ofthe flex connectors closer to the midpoint of the radial ring one canaddress foreshortening in an controlled fashion. In fact, ballooninteraction aside, the connector does not have to stretch to compensatefor foreshortening. When the flex connectors are connected at themidpoint of the radial ring, the distance/length through the middleportion of the stent between radial rings will remain unchanged. This isbecause the midpoint stays relativiely in the same position while theradial arcs of each strut move closer to the midpoint from both sides.By moving the location of the flex connector attachment beyond themid-point of a strut, to the opposing side, one can actually capitilizeon the strut moving closer to the midpoint and thus lengthen the stentupon expansion.

In addition, in the present embodiment described, adjacent radiallyrings start out of phase in the unexpanded state. Due to the diagonaloreintation of the connection points of the flexible connectors, uponexpansion the radial rings tend to align themselves (“in” phase.) Thisresults in more uniform cell space and thus improved scaffolding of thevessel. Further, there is described a “wavy” strut configuration,thereby facilitating both a reduced crimp profile for attaching theflexible connectors at or near a strut mid-point and reduced strain uponexpansion, due to the strut itself contributing to a portion of theexpansion.

Finally, a new method is disclosed for making stents. In this methodthere is novel photochemical machining of a cylindrical tube. The methodconsists of performing a standard photochemical machining process ofcutting, cleaning and coating the tube with a photoresist. However,unlike former methods, the photoresist image is developed on the surfaceof the cylindrical metallic tube, which results in a controlled variableetching rate at selected sites on the cylindrical metallic tube duringthe etching process. The photoresist image consists of a series ofcircular regions of photoresist of varying diameters configured atvarying distances along the stent. As the diameter of the circularphotoresist pattern decreases and the distance between the circularphotoresist patterns along the stent increases, the etch rate of thedevice increases. The photoresist pattern variation results in avariation in the metal removed during the etching process.

This process can be used to locally change the geometry of thecylindrical metallic tube. An advantage seen by this process is theability to manufacture a tapered strut along the stent. Further, strutsof cylindrical or other non-rectangular cross-section can bemanufactured. In addition, surface contours can be placed on the stent,for instance, to allow for a reservoir to be placed in the stent todeliver drugs.

These and further objects of the invention will be seen from thefollowing drawings and Detailed Description of the Invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a stent embodying the invention;

FIG. 2 and 3 are plan views of an alternative embodiment of a stent ofthe invention;

FIG. 4 is a plan view of yet another embodiment of a stent of theinvention;

FIG. 5 is a close up of the identified section of FIG. 4 taken alonglines b—b of FIG. 4;

FIG. 6 is a schematic of a photoresist pattern formed on the stent inorder to perform a method for making the stent as described in theinvention;

FIG. 7 is a plan view of yet another alternate embodiment of the presentinvention;

FIG. 8 is a plan view of a further alternate embodiment of the presentinvention; and

FIGS. 9 and 10 are schematics of the theory behind expansion of thestent of FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION

As can be seen in FIG. 1, there is described a cylindrical stent 10which has a series of folded strut sections 20 connected by a series offlexible sections 30. The folded strut sections 20 comprise a generallyfolded strut member 25 having a pair of ends 24, 26. Each of the pair ofends 24, 26 is connected to another folded strut member 25 and also tothe end of a flexible member 35. Thus, each end 34, 36 of a flexiblemember 35 is connected to two ends 24, 26 of a folded strut 25 sectionmember.

Each of the folded struts 25 takes on a generally irregular pattern. Onthe other hand, each of the flexible sections 35 takes on a generallyundulating pattern. The folded strut sections 20 wrap circumferentiallyaround the cylindrical shape of the stent 10. Each flexible section 30also connects to a folded strut section 20 around the circumference ofthe stent. It will be noticed that each adjacent flexible section 30 ispositioned 180° out of phase with each other.

The longitudinal lengths of the folded struts 20 are short enough togive a smooth profile when the stent is bent. The folded strut 20 allowsfor a large diametrical expansion range upon expansion. So, uponexpansion, the folded struts 20 expand circumferentially and becomehoop-like so that maximum radial strength is achieved. The flexiblemembers 30 placed between the folded struts improve the stentdeliverability in the unexpanded dimension of the stent 10. Theseflexible members are longitudinally compliant so that foreshortening isminimized upon expansion.

In use, therefore, the stent 10 of the present invention is placed on aballoon catheter and is snaked through the vasculature to be placed intoa lesion site in an artery, typically a coronary artery. Because theflexible sections 30 are so substantially flexible, they are able tonavigate tortuous lesions with relative ease. Once in place, the ballooncatheter is expanded by conventional means. Upon expansion, the struts25 in the folded strut sections 20 expand to obtain a hoop-like shape.In addition, these members expand longitudinally, so that any reductionin foreshortening is negated. Of course, upon expansion, the flexiblemembers 35 straighten so that there is further strength achieved by thestent in the straightened and rigid positions.

A variation of the present invention can be seen in the stent 50 ofFIGS. 2 (“angled” version) and 3 (“straight” version). There, the radialstrength sections 120 are achieved with generally straight members 115,although these members do not have folded struts. Connection betweengenerally straight members 115 is made by connecting the generallystraight members 115 to the more flexible members 125, much like theconnection made involving the connecting members of the first embodimentof FIG. 1.

The members that reduce foreshortening are angled members 130 which areseen to be 180° out of phase with one another. The connection betweenthe flexible members is made at the end of a particular relativelynon-flexible member and at the distal end of a particular angled cantedmember 130. Now, when the columns comprised of relatively rigid members115 expand, the length of these members 130 shorten. But, thelongitudinal lengths of the canted members 130 are placed at an anglecompared to the longitudinal axis of the stent 50. So, upon expansion,these canted members 130 actually lengthen with respect to thelongitudinal axis of the stent 50. The net result is that noforeshortening occurs upon expansion of stent 50.

The canted members 130 are angled in order to both: increaseflexibility; and to provide additional resistance on the balloonsurface. This arrangement helps prevent what is known as “dogboning” orexposure of leading edge of any of the strut members 75 contained ateither end of the stent 50. In addition, this configuration alsoprevents slippage of the stent along the balloon surface. The cantedmembers 130 are canted in opposite phase (i.e., with a phase change of180°) to one another, in order to negate any torsional effects on thestruts 75,85 along the length of the stent. These particular members canbe crimped to a lower profile than the more rigid members, in order toensure increased retention of the stent on the surface of a ballooncatheter. Further the configuration described herein has a uniquelyfolded configuration reducing any risk of “flaring” of the edges ofstruts 75, 85 during traversal of the lumen.

It is to be noticed that the longitudinal position (the “order”) of thecolumns can be changed if one desires a smaller initial profile. Thatis, if one desires that the profile be smaller, it is possible to removethe more rigid sections 120 (or a portion thereof,) and replace themwith the generally canted sections 130.

It is also to be noticed that the wave amplitudes of the struts in aparticular column are not kept constant. The wave amplitudes, definedherein as “W,” can be lengthened where permitted by the geometry. Forinstance, notice the space S created between one set of strut members Aand a second set of strut members B. This particular configurationallows an increased expansion range around the unexpanded circumferenceof the stent, while maintaining an appropriate expansion area associatedwith the metallic struts placed around of the circumference of thestent. Such optimization of the strut surface area is important toensure adequate coverage of the lesion upon expansion of the stent.

The stent 50 of this particular embodiment is expanded in much the sameway as the stent 10 of FIG. 1. When expansion occurs via the ballooncatheter, the canted members 130 tend to lengthen and preventforeshortening of the stent 50; the relatively rigid members 120 tend toshorten in the longitudinal direction, but in so doing provide a greaterrigidity for the fully expanded stent. It is to be understood however,that in the expansion of both stents 10, 50 the ability to flexiblynavigate the vasculature is enhanced from configuration of either stent10, 50, as the case may be. All the while, the likelihood of stentforeshortening upon expansion is greatly reduced.

As can be seen in FIG. 3, one can also provide for a stent 175 that doesnot contain canted sections. Yet, the stent 175 expands with decreasedforeshortening along its length due to the unique geometry of the stent175. Here, the stent struts 180, 190 provide for a relatively constantlength along the longitudinal axis. (In other words, the longitudinaldimension of the struts 180, 190 in combination remains relativelyconstant, whether in the expanded or unexpanded condition.) In thisfashion, upon expansion, the stent 175 maintains a generally constantlength in any of its expanded, unexpanded or partially expandedconditions.

FIGS. 4 and 5 show yet another embodiment of the design of a similarstent 200. Here, the connector 250 is shaped like an “N,” much after thesame fashion of “N”-shaped connectors found commercially in the BxVelocity® stent sold by Cordis Corporation, Miami Lakes Fla. and whichis at least somewhat characterized in Ser. No. 09/192,101, filed Nov.13, 2000, now U.S. Pat. No. 6,190,403 B1, and Ser. No. 09/636,071, filedAug. 10, 2000, both of which are assigned to Cordis Corporation, andincorporated herein by reference.

In the stent 200, the relatively rigid sections R contain unequal struts210, 220 of lengths a, b, as can best be seen in FIG. 4. Moreover, ascan be seen in FIG. 5, this strut pattern is formed so that theattachment points a at the end of the flexible connectors 250 can belocated at any point along the struts 210, 220 rigid section. In thisfashion, when the stent is expanded, the relatively more rigid section R“holds” the connector 250 along the surface of the lesion, so thattenacity of the stent, and its concomitant support are both maintainedto a high degree at the situs of the lesion. Yet, in the unexpandedconfiguration, the “N”-shaped flexible connectors 250 are able to guidethe stent 200 around the curvature of generally any tortuous vessel,including tortuous coronary arteries.

As can be seen from FIGS. 4 and 5, the alternative embodiment stent 200is also capable of reducing foreshortening along its entire length. Thisstent contains relatively rigid sections R and relatively flexiblesections F containing connectors 250. (The flexible sections F are inthe form of undulating longitudinal connectors 250.) The relativelyrigid sections R generally contain a slotted form, created with struts210, 220 around a slot S. The relatively rigid sections R contain theseinterlaced struts 210, 220, which are of varying longitudinaldimensional length.

As can be seen from the figures, in some radial positions, the struts210 are made longer. In other radial positions, the struts 220 are madeshorter. However, the shorter struts 220 are of a constant length b inthe longitudinal dimension, and in the fashion in which they connect tothe relatively flexible connectors 250. Also, as described above, therelatively more rigid sections R maintain the relatively more flexiblesections F at a generally constant longitudinal length due to thefriction maintained by the relatively more rigid sections R on a balloonportion of an angioplasty type balloon catheter. Accordingly, uponexpansion, the constant length b, in conjunction with the generallyconstant length of the relatively flexible connector 250, causes thestent 200 to maintain a relatively constant longitudinal dimension L inany diameter to which it is expanded. As can be appreciated, themaintenance of a constant length is desirable from the perspective ofsecure, repeatable placement of the stent within the vasculature.

Continuing to describe the stent 200 of FIGS. 4 and 5, the flexiblesections F operate with the behavior of the flexible connectors 250acting in the fashion of “N”-shaped flexible connectors of similar type.That is, the flexibility of the stent 200 is focused in this area F sothat one is able to traverse tighter lesions using such a configuration.The relatively stronger sections R are capable of expansion to astronger plastically deformed dimension, so that in this fashion thestent 200 is capable of supporting the arterial wall. Even though thelongitudinal dimensions of the struts 210, 220 in the relativelystronger sections R are of unequal length, such a configuration does notdiminish radial support in the expanded condition. Accordingly, it canbe appreciated that a stent of this shape will adequately support thearterial walls at the lesion site, while maintaining radial flexibility,and longitudinal length.

As can be best seen in FIG. 7, yet another alternate embodiment of thepresent invention is described. In FIG. 7, there is contained a stent300 much like the Bx Velocity® stent sold by Cordis Corporation, MiamiLakes, Fla. In FIG. 7 there is contained on the stent 300 generallyflexible connector members 310 connected to generally rigid radial strutmembers 320. The connector members 320 are generally formed in the shapeof the letter “N”, and the struts 310 are generally slots formed in aradial fashion around the circumference of the stent. The connectionmade between the flexible connectors 320 and the radial strut members310 is formed from a living hinge 330. This living hinge 330 containsouter radial arc 332 and an inner radial arc 334. In the expandedconfiguration, the radial arcs 332, 334 move away one from the other, sothat the overall length of the living hinge 330 actually increases uponexpansion.

Known conventional means, such as angioplasty balloons, or the balloonon a stent delivery system expands the stent 300 of the presentinvention. Upon expansion, there are provided a number of benefits bythe stent 300 of the present invention. First, as explained above, thereis reduced foreshortening of the stent 300, since the outer radial arc332 in fact does not foreshorten. Since it lengthens slightly, theoverall length of the stent 300 is maintained to its general nominallength. There is also provided increased radial strength since theradial arcs 332, 334 at their connection between the flexible and radialstruts 320, 310, (both inner and outer radial arcs 334, 332) combine togive superior strength in the arcs' section; the radial strut 310provides for optimal strength in the radial direction since it isparallel to the loading direction of the stent 300, thereby creating a“hoop” a circumference C of the stent. Also, because the radial arcs areable to accept greater forces, there is reduced strain for theequivalent strength designed for a stents. In all, the stent 300 of thisembodiment provides for at least equivalent radial strength, lessforeshortening and reduced strain when compared to current stents.

As can be seen from FIGS. 8, 9 and 10, there is provided yet anotherembodiment of the stent 400 in the present invention. Again, the stent400 provides for generally stronger radial sections R comprising radialstruts 410, which are generally slotted in alternating fashion aroundthe circumference of the stent. The flexible connector members 420 aresimilar to the flexible connector members as seen in FIG. 7, and also tothe flexible connector members of the Bx Velocity® stent. However, theseflexible connector members 420 are connected to the radial strutsgenerally somewhere near the midpoint of the radial struts 410. In thisfashion, upon expansion the length of the connector members 420 remainsindependent of the shortening or lengthening of the radial struts 410.In this way, the overall length of the stent is maintained, as seen fromthe schematics in FIGS. 9 and 10.

Due to this overall ability to maintain the length of stent 400, theradial struts 410 provide for radial strength only, and do notcontribute in one way or another to any foreshortening of the stent.Also, the radial struts 410 are formed from a generally “wavy” pattern.This wavy pattern is useful in helping to reduce the crimp profile ofthe stent 400 on the balloon. This results from the relative smoothattachment of the radial struts 410 to the flexible connectors 420.Further, having such an arrangement reduces the strain placed on thestruts 420 upon expansion. This reduced strain is achieved due to thelocation of the connection of the struts 420 to the struts 410. Becausethere is relatively little movement of the struts 420 in thelongitudinal direction, there is relatively little strain placed onthese struts during expansion. The radial arcs 415 of struts 410 can beideally placed in a “shifted” configuration so that the stent is easierto crimp on a balloon.

Further, this can be seen from FIG. 8, that the radial strut members 410are attached to the flexible connectors 420 so that the flexibleconnectors 420 generally proceed along a “spiral” pattern S around thelength of the stent 400. The connection points 422 of the flexibleconnectors 420 are placed in a diagonal fashion on struts 410 so as toenhance flexibility. Generally connectors 422 are located on a midpointof a strut 410. When the connectors 422 are placed past the midpoint ofstrut 410 (i.e., farther from the midpoint of strut 410 than from thedirection of connector 420), the nominal stent strength should increaseupon expansion when compared to the above described stent. Thisarrangement reduces foreshortening, as described above. Further, thearrangement in no wise affects any torsion on the stent as it is appliedto the lumen by the balloon catheter. Friction of the balloon to struts410 maintains the struts 410 (and their opposite struts 420) in the samegeneral radial position throughout expansion. By reducing any concern ofstent torsion, there is also a reduced concern of overall slippage ofthe balloon. Even though the connector members 420 are not aligned withone another, they are maintained in their respective positions on theballoon surface. Upon expansion, struts 420 lock into place, as thestent 400 is placed, giving an increased strength in the lumen.

From FIGS. 8 and 9, we see that the midpoint of a connector 420 isimportant to maintaining length. The greater the distance from connector420 to the midpoint M, on the side of the connection between struts 410,420, the greater the potential for shortening of the stent. This createsa need to solve any shortening by other means, absent the solutiondescribed herein.

It is to be understood that various modifications to the stent 400 ofFIGS. 8, 9 and 10 are possible without departure from the inventionherein. For instance, the connectors 420 can be placed intermittentlyabout the stent 400 circumference, and not at every incidence of aradial strut 410. Also, while the radial struts 410 are generally 90°out of phase between one series of struts 410 a and the next 410 b, itis foreseeable to place them between 30° to 150° out of place. When soplaced, the struts 410 can be “encouraged” to bend in a particularfashion, which may be preferential in the design of a particularlyintended stent.

These stents can be manufactured by know conventional means, such aslaser etching, electrical discharge machining (EDM), photochemicaletching, etc. However, there is also disclosed in the invention herein anovel method of performing photochemical resistance etching of the tubefrom which the stent is to be made. This novel method allows one toproduce a stent with variable geometry in the three dimensions of thestrut, that is, along its length, across the circumferential dimension,and along its depth (or radial dimension.) This method starts with astandard photochemical machining process.

The new process consists of cutting the stent using photochemicaletching, cleaning it, and then coating it with a photoresist. Thephotoresist coating is applied in circular shapes 290, as can beappreciated from FIG. 6. These shapes 290 are intentionally figured tobe of varying dimension in their radius. Then, a photoresist image isdeveloped on the surface of the cylindrical metallic tube T from whichthe stent starts. This photoresist image is developed in a controlledfashion using known means. The development of the photoresist in thisfashion allows a controlled variable etching rate at select positionsalong the cylindrical metallic tube.

As previously stated, the novel photoresist image can be seen in FIG. 6.This photoresist image consists of a series of circular regions ofphotoresist material 1310, which are shaped in a variable diameter asdesired for manufacture. These photoresist images 1310 are configured atvariable distances D from one another. As the diameter of the circularphotoresist pattern 1310 decreases, and its distance from otherphotoresist patterns 1310 increases, the etching rate of that area ofthe stent increases. Thus, by strategically placing the photoresistpatterns 1310 on the stent, one can produce any variable dimension inany direction along the stent.

This photoresist pattern 1310 variation results in a variation in themetal of the stent removed during the etching process. This process canbe used to locally change the geometry of the metallic tube.

In this fashion, one can envision making a stent of variablecircumferential width, radial depth or longitudinal length. As such, onecan impart varying flexibilities along the stent longitude, as well asvarying strengths so that a stent can be configured for emplacement atvarious locations within the body.

1. A method for manufacture by controlled variable etching, of a stentwith struts having varying strut thicknesses, said stent having agenerally tubular configuration with a longitudinal axis and a generallythin wall containing said struts therein, said method comprising:creating a plurality of photoresist images of varying size on thesurface of a preformed stent, said photoresist images placed on saidstent according to varying configurations; etching a pattern of strutson said stent around said plurality of photoresist images on the surfaceof said stent, said photoresist images placed on said stent according tosaid varying configurations, such that said resultant stent containingsaid etched pattern has different strut thicknesses along the stentlongitudinal axis.
 2. The method of making a stent as described in claim1, further comprising the stent having a plurality of struts, and saidstent formed with a plurality of struts tapered in radial thickness. 3.The method of making a stent as described in claim 1, further comprisingthe stent having a plurality of struts, and said stent formed with aplurality of struts variable in radial thickness.
 4. The method ofmaking a stent as described in claim 1, further comprising the stenthaving a plurality of struts, and said stent formed with a plurality ofstruts contoured along their length.
 5. The method of making a stent asdescribed in claim 1, further comprising the stent having a plurality ofstruts, and said stent formed with a plurality of struts non-rectangularin cross-section.